Virtually all known bicycle hydraulic disc brake master cylinders operate in the same basic way. A piston is movable within a cylinder from a start position near a first end of the cylinder to a pressurized position near a second end of the cylinder. Between the first and second ends of the cylinder is a timing port in fluid communication between the cylinder interior and a hydraulic fluid reservoir. As the piston moves from the start position toward the timing port, hydraulic fluid flows from the timing port to the reservoir. Once a seal associated with the piston moves between the timing port and the second end of the cylinder, fluid within the second end of the cylinder and hydraulic lines in fluid communication with a caliper become pressurized and the caliper is actuated. The travel between the start position of the piston and the timing port is known as the “dead-band”.
Different structures are known for varying the amount of dead-band in accordance with user preferences. For example, it is known to physically alter the start position of the piston within the cylinder to vary the dead-band. However, such structures also result in movement of the start position of a lever handle operatively associated with the piston. This results in variation of the “reach” between the handle and the handlebar. This can be bothersome to riders and require the riders to readjust the reach after changing the dead-band.
The present invention is directed to overcoming one or more of the problems discussed above.